1. Field of the Invention
The present invention relates to a battery pack in which four cylindrical battery cells are arranged in two rows and two layers and are connected in series.
2. Description of the Related Art
A battery pack includes a plurality of cylindrical battery cells, electrode tabs for electrically connecting terminals of the battery cells arranged in a certain pattern, a lower case for containing the battery cells electrically connected through the electrode tabs, and an upper cover for covering the lower case containing the battery cells therein, and is detachably attached to an electronic apparatus such as a video camera for private use, to be used as a power source for the private-use electronic apparatus (refer to Japanese Patent Laid-Open No. 2003-257388).
Battery packs to be used in electronic apparatuses such as video cameras for private use according to the related art needs a rated voltage of about 7.2 V. Meanwhile, a battery cell composed of a cylindrical lithium ion secondary cell, for example, has a rated voltage of about 3.6 V. In the related art, therefore, in order to realize the rated voltage of about 7.2 V, four such battery cells are arranged in two rows and two layers, the battery cells in each set of paired battery cells are connected in parallel through a main circuit board, and the two sets of the parallel-connected paired battery cells are sequentially connected in series.
However, the so-called S-size battery packs composed by use of four battery cells do not include those for use in electronic apparatuses for business use, i.e., those which realize the rated voltage of about 14.4 V. Therefore, there has been a request for an S-size battery pack which is lighter in weight than the so-called L-size battery pack composed by use of eight battery cells according to the related art, and which realizes the rated voltage of about 14.4 V suitable for use as a power source for business-use electronic apparatuses.